linux-kernel - Re: [PATCH v1] PM: sleep: Do not flag runtime PM workqueue as freezable

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Message-ID: <CAJZ5v0iNGq-O9pbKaGGiqiY-xD7qndXkJ8oCdTxkuWE8CxLQ=w@mail.gmail.com>
Date: Tue, 2 Dec 2025 14:29:51 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Bart Van Assche <bvanassche@....org>
Cc: YangYang <yang.yang@...o.com>, Jens Axboe <axboe@...nel.dk>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v1] PM: sleep: Do not flag runtime PM workqueue as freezable

On Tue, Dec 2, 2025 at 12:53 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Tue, Dec 2, 2025 at 2:06 AM Bart Van Assche <bvanassche@....org> wrote:
> >
> > On 12/1/25 11:58 AM, Rafael J. Wysocki wrote:
> > > So I've been testing the patch below for a few days and it will eliminate
> > > the latter, but even after this patch runtime PM will be disabled in
> > > device_suspend_late() and if the problem you are facing is still there
> > > after this patch, it will need to dealt with at the driver level.
> > >
> > > Generally speaking, driver involvement is needed to make runtime PM and
> > > system suspend/resume work together in the majority of cases.
> >
> > Thank you for having developed and shared this patch. Is the following
> > quote from the Linux kernel documentation still correct with this patch
> > applied or should an update for Documentation/power/runtime_pm.rst
> > perhaps be included in this patch?
> >
> >   "The power management workqueue pm_wq in which bus types and device
> > drivers can
> >    put their PM-related work items.  It is strongly recommended that
> > pm_wq be
> >    used for queuing all work items related to runtime PM, because this
> > allows
> >    them to be synchronized with system-wide power transitions (suspend
> > to RAM,
> >    hibernation and resume from system sleep states).  pm_wq is declared in
> >    include/linux/pm_runtime.h and defined in kernel/power/main.c."
>
> It doesn't say what the synchronization mechanism is in particular and
> some synchronization is still provided after this patch, via the
> pm_runtime_barrier() in device_suspend(), for example.

Though there is another piece of documentation that needs updating to
reflect the changes in this patch, so I'll send a v2 at one point.